Types (Junior Cert Wood Technology): Revision Notes
Plastics Overview
This section provides crucial definitions that students should familiarise themselves with to grasp the fundamentals of plastics in wood technology.
Definitions
- Thermoplastics: Soften with heat and harden when cool; can be reshaped multiple times.
- Thermosetting Plastics: Harden permanently with heat and cannot be reshaped.
- Acrylic: A clear and strong thermoplastic.
- Polyurethane: A durable and tough thermosetting plastic.
Main Types of Plastics
Thermoplastics
Thermoplastic polymers (or thermoplastics) are modern synthetic polymers that have been developed over the past century. They include popular materials such as acrylic (Perspex), polythene (used for plastic bags), and polypropylene (used for plastic chairs).
The key characteristic of thermoplastics is their ability to become flexible when heated and rigid when cooled. This property makes them extremely useful for manufacturing and recycling processes.
Thermosetting Plastics
Thermosetting polymers (also called thermosets) are fully synthetic polymers that behave very differently from thermoplastics. Common examples include Bakelite and epoxy resins. These materials undergo a permanent chemical change during their formation, which gives them unique and irreversible properties.
The key distinguishing feature of thermosets is that once they are formed and set, they cannot be reheated and remoulded like thermoplastics can. This makes them ideal for applications where permanent shape and heat resistance are essential.
Examples of Plastics
Thermoplastics Examples
- Acrylic (Thermoplastic): Clear and strong; used instead of glass in windows and lenses.
- Other examples: PVC and Polystyrene; used in pipes, packaging, and containers.
Thermosetting Plastics Examples
- Polyurethane (Thermosetting): Used in foam seating; cannot be reshaped once set.
- Other examples: Epoxy resins and bakelite; used in car bodies and electrical insulations.
Practical Use and Benefits over Wood
- Plastic Benefits:
- Flexible
- Durable
- Resist moisture and pests
- Compared to Wood: Plastics offer better durability and resistance.
- Acrylic thermoplastics are a recyclable and lightweight alternative to glass and wood in windows.
- Thermosetting plastics like polyurethane resist heat where wood would not last.
- Example Table:
Property Plastics Wood Durability High Moderate Water Resistance High Low Flexibility High (varies) Low Maintenance Ease Easy Varies (depends on type)
Summary
- Thermoplastics are flexible, reshaped many times, and recyclable.
- Thermosetting plastics resist heat and are strong; cannot be reshaped.
- Examples like acrylic and polyurethane show the strengths of plastics over wood.
- Plastics usually provide better durability and resistance than wood.